Determining an amount of air entering an engine, and in particular an amount of air in cylinders of the engine, is important for various aspects of engine control, including regulating emissions and fuel consumption. Due to airflow dynamics at the throttle versus the cylinders, aircharge is frequently estimated based on the manifold absolute pressure (MAP), which may be measured with a sensor. However, the MAP will continuously vary throughout the operation of the engine. U.S. Patent Application No. 2013/0066535 A1 describes a method for the determination of aircharge using a pressure sensor located between the air intake port of a cylinder and a port throttle, and a method comprising pressure measurements for each firing cycle in each cylinder at or near intake valve closing time. The referenced application determines the air pressure at intake valve closing (IVC), or at the closest instance possible. Thus measurement of the MAP at IVC results in accurate estimation of the air pressure within the cylinder.
However, the inventors herein have recognized an issue with the above approach. In order to sample the MAP sensor at IVC, an interrupt may be generated by the engine control unit (ECU) at IVC to trigger sampling and/or processing of the MAP sensor signal. Alternatively, the MAP sensor may be sampled at even increments of engine crank angle, and then the samples may be analyzed to determine which sample was taken at or close to IVC. Either method, however, is computationally expensive and may not be feasible with current ECU architectures. Further, such methods may lose accuracy and/or require even more computation resources during transient operation, e.g., when engine speed is increasing.
Accordingly, the inventors herein provide an approach to at least partly address the above issues. In one example, a method includes sampling an intake manifold pressure sensor signal at even increments of time, storing each sampled signal in a buffer, processing the stored sampled signals in the buffer at even increments of engine crank angle, and adjusting a fuel injection amount based on a selected one of the processed sampled signals.
In this way, an intake manifold pressure (MAP) sensor signal is sampled at even increments of time and each sampled signal is stored in a buffer. Each of these MAP sensor samples may be stamped with the corresponding angle of the crankshaft at time of sampling. Concomitantly, the presented commanded or actual position of IVC is also noted. When the aircharge is to be computed (e.g., once per firing period), the MAP sample with an angle stamp closest to IVC is retrieved from the buffer. This MAP signal may be used to compute aircharge for a particular cylinder. Once the aircharge of the cylinder is determined, the proper injection amount of fuel may be computed. The disclosed method overcomes the incapacity of existing ECUs to both sample and process sensor signals at fine increments of a crankshaft angle (e.g., 6 crankshaft degrees). Using an angle stamp for each MAP signal that is sent to a buffer circumvents the need to have a controller-interrupt at pre-specified angles because each sample does not need to be processed immediately. The processing may be carried out when the next cylinder firing event is about to take place (for example, every 240° on a three cylinder engine). Thus, accurate estimation of aircharge may be provided while minimizing the processing power required for estimating the aircharge.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.